Technical Field
The present invention in certain embodiments relates to the refrigerator industry, and in particular relates to cryogenic regenerators and cryogenic refrigerators.
Description of Related Art
Pulse-tube refrigerators are regenerative refrigerators that gain refrigeration by the principle of temperature decrease due to adiabatic expansion of a gas. Mainstream pulse-tube refrigerators at present are divided according to their drive scheme into two categories, Gifford-McMahon (GM) pulse-tube refrigerators and Stirling pulse-tube refrigerators, wherein according to needs, double-inlet installations may be appended to the GM types and to the Stirling types.
A Stirling pulse-tube refrigerator as illustrated in FIG. 1 includes, in connected order, a compressor, a transport pipe 1, a cooler 2, a regenerator 3, a cold-end heat exchanger 4, a pulse tube 5, a hot-end heat exchanger 6, an inertance tube 7, and a reservoir 8, while a Stirling pulse-tube refrigerator having a double inlet is further provided with, as illustrated in FIG. 2, a gas inlet tube 10 having an inlet valve 9, wherein one end of the inlet tube is connected to the transport pipe, and the other end is connected to the hot-end heat exchanger.
A GM pulse-tube refrigerator as illustrated in FIG. 3 includes, in connected order, a transport pipe 1, a cooler 2, a regenerator 3, a cold-end heat exchanger 4, a pulse tube 5, a hot-end heat exchanger 6, an inertance tube 7, and a reservoir 8; here, the cooler is connected to a high-pressure gas source via a first gas pipe, and connected to a low-pressure gas source via a second gas pipe, with the first gas pipe and the second gas pipe both being provided with an electrically actuated valve, while a GM pulse-tube refrigerator having a double inlet is further provided with, as illustrated in FIG. 4, a gas inlet tube 10 having an inlet valve 9, with one end of the inlet tube being connected to the transport pipe, and the other end being connected to the hot-end heat exchanger.
The working processes of a pulse-tube refrigerator are as follows. When compressed gas from the compressor enters into the refrigerator (with GM types a high-pressure gas source is connected to the refrigerator), the gas, having gone through a prior-stage precooling process in the cooler as well as a precooling process in the regenerator, enters into the pulse tube, where the heat of compression is discharged by the hot-end heat exchanger. When the gas begins to expand and returns to the compressor (with GM types a low-pressure gas source is connected to the refrigerator), the gas adiabatically expands in the pulse tube 5, whereby the temperature drops, and at the same time the refrigeration is transferred by the cold-end heat exchanger 4, with the regenerator being precooled by the remnant refrigeration. Herein, as a core among the components, the regenerator 3 has a critically important impact on the efficiency and refrigerating capability of the refrigerator.
With conventional large-capacity pulse-tube refrigerators, there are problems, originating in the augmentation of the geometric size of the regenerator, unique to large-capacity pulse-tube refrigerators, with the most typical being that of non-uniformity phenomena inside large-diameter regenerators. Non-uniformity phenomena, due to flows in the regenerator interior and to positive heat-conduction feedback, are phenomena in which the heat regenerating efficiency abruptly deteriorates. The mechanism giving rise to non-uniformity phenomena is exceedingly complex, and is one in which linearly streaming flows reciprocate between the cold end and the hot end inside the regenerator, and is characterized by the temperature of the regenerator along its periphery having a pronounced temperature gradient. This in actuality produces a drastic reduction in the effective volume participating in the cooling cycle inside the regenerator, while with the linearly streaming flows, heat energy at the hot end also is introduced into the cold end, increasing losses inside the regenerator and furthermore, producing an abrupt drop in regenerator efficiency. Research has brought to light the fact that regenerators in which non-uniformities are kept under control achieve a cooling capability generated by the refrigerator that is five times that of refrigerators in which non-uniformities are not kept to a minimum. As will be appreciated from this, keeping non-uniformities under control holds critically important significance for large-capacity pulse-tube refrigerators.
Currently, the method of keeping non-uniformities under control is to have increasing the same cross-sectional heat transfer be the expedient, which means inserting high thermal-conductivity packing into the middle stage of the regenerator. For example, Chinese Patent CN1971172 discloses a regenerative heat exchanger of enhanced radial heat conductivity, which includes a regenerator housing and, placed in alternation inside the regenerator housing, perforated metal plates and metal meshes/lead spheres whose heat conductivities differ. However, with this approach, axially directed heat conductivity inside the regenerator increases such that subsequent heat conduction losses in the regenerator also increase. Currently reported regenerators ordinarily must be able to withstand temperature gradients whose temperature differences exceed 220 K over distances of less than 100 mm, on account of which metal packing for increasing the axial heat conductivity has not been the optimal choice for the regenerator.
Large-capacity pulse-tube refrigerators are adopted chiefly in industrial areas such as diverse high-temperature superconductors, and lossless reservoirs for cryogenic fluids, which include superconducting motors, superconducting generators, superconductive current limiters, superconductive leads, and large-scale cryogenic fluid-reservoir tanks. Since they are subject to the limitations of factors including regenerator efficiency, large-capacity pulse-tube refrigerators currently are of overall efficiency that, as before, is not high, thus, higher efficiency regenerators are predisposed to future development.